Walter Russell Mead doesn’t think  denuclearization of North Korea is an unrealistic goal:
All this is to say that the effort to denuclearize North Korea is an uphill climb. That does not mean the effort is futile or should not be made. Sometimes diplomacy is about taking a series of small steps without having the summit in view. As you trek patiently upward, new paths appear—and new choices have to be made.
Mead doesn’t explain why pursuing denuclearization isn’t futile, but just takes for granted that it isn’t. There is intense resistance among American policymakers and pundits to admit that it is never going to happen, the longer it takes us to acknowledge reality the harder it will be to craft an appropriate, relevant policy to address that reality. When a policy goal is unreachable, or if it can be reached only at extraordinary cost, it is incumbent on supporters of the existing policy to recognize that it can’t work and make the necessary changes to adapt it accordingly. There may be times when stubborn persistence pays off, but this isn’t going to be one of them.
Admitting that the last two and a half decades of North Korea policy have failed is not an appealing prospect, but we have long since passed the moment when we needed to reach that conclusion. To borrow Mead’s image, trudging up a mountain when the peak cannot be reached safely is neither admirable nor smart. It is a dangerous obliviousness to the pitfalls of continuing on the current path. The U.S. should stop listening to the people urging our government to keep marching blindly ahead towards a goal that will always remain out of reach.
Besides the embarrassment of failure, why is there such an aversion to accepting that denuclearization won’t happen? It is not because the U.S. has never had to cope with a hostile, nuclear-armed state before. The U.S. has been facing far larger threats from nuclear-armed, hostile dictatorships for decades, and it has managed those threats successfully all this time. I suspect that many people insist on denuclearization out of habit, others echo this line simply because it is the consensus view, and all of them prefer not to challenge that consensus for fear of being seen as “soft” on North Korea. My guess is that the fear of not appearing “tough” has a lot to do with this clinging to an impossible goal. For many policymakers and pundits, it is politically safer and easier to endorse a policy goal that can’t be achieved because it is considered “tough” even if it creates a more dangerous situation for the affected countries. Our foreign policy debates create and reinforce these perverse incentives, and our diplomacy needlessly suffers as a result.